Cadmium plated, non-breakable heavy duty housing resists rust, and gives long life in most any environment. Isolates the starting battery, assuring you of primary battery power for starting the engine. Has full time charging of both batteries. Includes terminal nuts and lock-washers. For 12VDC continuous duty.7000S: 3 Terminal model for metal frame ground systems.7001S: 4 Terminal model has insulated ground terminal for use with fiberglass or other non-conductive materials.